A Grand Star
Grand Stars are large Power Stars found in Super Mario Galaxy and Super Mario Galaxy 2. They typically appear after Mario defeats Bowser or Bowser Jr.. These will help players to progress through the games.
In Super Mario Galaxy collecting Grand Stars enabled Mario to reach other areas in the game. One would be collected every time he defeated Bowser or Bowser Jr.
In Super Mario Galaxy 2 Grand Stars return and play the exact same role. Every time Mario would defeat Bowser or Bowser Jr. one would appear for him to collect. These Grand Stars than gave his star ship the power to reach new areas.